To enter Mauritius citizens of most of the European countries will need only a 6 months valid passport, a return ticket and an address during their stay in the country. If you are not sure, better contact the Mauritian consulate in your country.
Maximum stay is 3 months but it might be that the immigration officer will issue you only 2 months. In case you want to stay the 3 months you have to visit the immigration office in Port Louis to extend your visa for one more month.
You will receive the necessary immigration documents either in the plane or at the airport in Mauritius (please do not forget your address in Mauritius – its needed at the immigration-counter).
Sometimes you find a copy for the departure enclosed to this document. Don’t worry in case you have lost the copy, you can fill in a form at the airport on departure.
In some older travel-guides a departure-tax is mentioned. Please note that this tax is now included in your flight-tickets. There is NO international airline whatsoever which requires reconfirmation of flight tickets despite what is written in old tourist guides.
On the Mauritius airport you can enjoy the duty-free-shop on arrival as well as on your departure (to spend your last Rupees).
Links concerning immigration and moving to Mauritius